7.3.2.2.2.2 MMC2 Signals Used for SD Card
Interface
The recommendation is to add a
series resistor (0Ω) for MMC2_CLK (close to processor clock output pins for
control of possible signal reflections). A pulldown (10kΩ) is recommended for
MMC2_CLK near to the attached device input to hold the clock in low state (there
are cases where the clock is stopped or paused in a low logic state and the
pulldown option is consistent with this logic state) until the host configures
the signal as clock.
The recommendations is to add
external pullup (47kΩ) for the SD card data signals (MMC2_DAT[3:0]) and CMD
signal (MMC2_CMD) to prevent the attached device inputs from floating until the
host software drives the interface signals. The recommendation is to connect the
SD card interface signals pullup to dual-voltage IO supply for IO group (MMC2 =
VDDSHV4) supply rail. 47kΩ pullup is recommended for data and command signals to
meet the SD card specification (in case internal pullups are unexpectedly
enabled the resulting pullup (47kΩ parallel to the internal pullup) value is
still within the resistance range specified in the relevant standards).
For supporting SD card interface,
the recommendation is to use MMC2_SDCD and MMC2_SDWP signals referenced (power)
to VDDSHV1. The recommendation is to connect the external pullup (10kΩ) for the
MMC2_SDCD and MMC2_SDWP signals to the same supply rail that is connected to
VDDSHV1 supply rail (close to attached device (SD card socket)).
SD Card Detect (SDCD) input to the processor connects directly to ground when
the SD card is inserted. A series resistor (100Ω) to limit the current in case
the IO is programmed as output unexpectedly is recommended.